Electric discharge device



Oct. 30, 1951 D. L. SMART ELECTRIC DISCHARGE DEVICE 2 Sl-[EETS-Sl-IEET l Filed Oct. 20, 1949 ooo 2 A ttorney! D. L. *SMART 2, ELECVTRIC DISCHARGE DEVICE 2 SHEETS-SI-[EET 2 nventor t torneys' Oct. 30, 13:31

Filed Oct. 20, 1949 Patented Oct. '30, 1951 ELECTRIC DISCHARGE DEVICE David Lorimer Smart, Staflord, England, assignor to The English Electric Company Limited, London, England, a British company Application October 20, 1949, Serial No. 122,&62 In Great Britain October 27, 1948 Claims.

This invention relates to' pool cathode electric discharge devices of the kind in which the envelope, at least in the region where the anode seal is made, is of vitreous material and which have a single main anode. It may also relate to similar multi-anode devices in which the anodes are mounted in the main body of the device and not in side arms.

In such devices considerable quantities of the cathode material are continually being vaporised by the action of the cathode spot, and this material will condense on any part of the device whose temperature is not maintained above a certain value, which depends on the pressure of the vapour. It is important that no appreciable quantity of cathode material should condense in parts of the device where gradual increments in the quantity of material so collected would eventually result in drops oi' the material falling on to the anode of the device, or intermittent spilling over of the material, giving rise to undesirable electrical characteristics.

According to the invention a pool cathode electric discharge device has an anode sealed through a re-entrant vitreous portion of its envelope and a tube surrounding said anode and clamped or sealed directly to said re-entrant portion, said tube being so shaped as to prevent the collection thereon of any appreciable quantity of.

liquid cathode material formed by condensation in the upper part of the device and so arranged as to ensure that such material returns to the cathode without penetrating the space between the tube and the anode. The tube may form part of a control grid and may consist of asubstantially regular cylindrical metal tube attached to the re -entrant portion of the envelope by means of a metal clamp and in order that the spacing between the anode and the tube may be made sufilciently large to prevent a flash-over in the case of a rectifier, the re-entrant portion of the envelope may be bulged outwardly in the region where the tube is clamped to it. The anode stem may be sealed to a narrowed izner end of the re-entrant portion by means of an intermediate metal cup and a shield may be provided around this seal. In an alternative arrangement the end of the re-entrant portion to which the anode stem is sealed may be turned back upon itself, thus reducing the total length of the device. In either case the design of the device and its cooling arrangements, i! any, must be such that no cathode material will condense on any portion of the envelope between the anode seal and the point where the tube is sealed or clamped to the envelope.

In order that the invention may be clearly understood several forms thereof will be described with reference to the accompanying drawings.

In Fig. 1, a tubular glass envelope l is provided with a re-entrant portion 2 having a narrow neck 3 to which an anode 4 is sealed by means of a metal cup 5. A grid tube G surrounds the anode 4 and its seal and is clamped by means of a metal clamp 'l on to the re-entrant portion 2 at an intermediate region 8 which is bulged outwardly to correspond with the internal di- A ameter of the grid tube 6. In order to prevent damage to the glass near the seal, due to being hit by high speed vapour ions, a shield 9 is provided attached to the anode stern. The reentrant portion 2 will attain a considerably higher temperature in operation than the remainder oi' the envelope i and, in the region between the grid tube 6 and the anode seal 5, condensation of cathode material will be substantially prevented. It is, however, desirable that condensation should take place in the upper portion of the envelope I in order that the general Operating temperature of the device may be kept within reasonable limits. Any condensation, however, which takes place in the upper part of the envelope where the re-entrant portion is joined to it will have no opportunity of collecting in any considerable quantity on the rid tube 6.

In Fig. 23 an alternative form of the invention is shown in which corresponding parts have been given the same reference numerals as in Fig. 1. In this case, however, the inner end 3 of the re-entrant portion of the envelope and the cup 5 which is sealed thereto is inverted. By this means the anode seal is brought nearer to the upper end of the device and the anode 4 is thus also raised. This results in decreased length oi' the device.

In Figs. 3 and 4 are shown further constructions embodying the invention and here again the same reference numerals as were used in Fig. 1 have been used for corresponding parts. In Fig. 3 the re-entrant portion 2 has attached to it a depending metal ring sa by means of a glass to metal seal and the grid tube 6 is fltted into the open end of the ring sa.

A shield 9 at anode potential is included to reduce heat radiaton from the anode to the glass in the region of the anode seal and to reduce the possibility of anode material being deposited on this glass. i

Fig. 4 shows a somewhat similar arrangement' but in this case the ring &a is fianged at its open &673,619

end and a corresponding flange formed on the tube i is secured thereto for example by spot welding. A shield sa in the form of an apertured metal disc is secured at the junction ot the tube 6 and the ring Sa. The shield !a is thus at grid potential.

Fig. shows an arrangement for a multi-anode device in which the envelope I is provided as before with a re-entrant portion 2 having three narrow necks 3 to each of which an anode 4 is sealed by means of a metal cup 5. A grid tube i surrounds all the.`anodes 4 and is' secured to the re-entrant portion 2 by means of a clamp The anodes 4 are separated by radial bame piates lil and are provided with individual shields 9.

The anodes may be of graphite or may be in the form of hollow` metal cups.

What I claim as my invention and desire to secure by Letters Patent is:

l. In a pool cathode electric discharge device including an envelope mainly of vitreous material, a tubular integral re-entrant portion on said envelope, an anode sealed through said re-entrant portion and a tube surrounding said anode supported directly on and forming with said re-entrant portion a seal impervious to liquid cathode material, the outer surface of said tube extending from said re-entrant portion always towards the cathode so as to prevent the collection thereon of any appreciable quantity oi' liquid cathode material.

2. The invention defined in claim I, wherein said tube forms part of a control grid for the device. V

3. The invention defined in claim 1, wherein said tube is substantially cylindrical throughout its length and is secured to said re-entrant portion by means of a constricting clamp.

4. In a pool cathode electric discharge device having an envelope mainly of vitreous material, a tubular integral re-entrant portion on said envelope, said portion being provided with a further narrower portion. an anode sealed through said narrower portion and a tube surrounding said anode supported directly on and forming with the wider reentrant portion a seal impervious to liquid cathode material, the outer surface of said tube extending from said wider re-entrant portion always towards the cathode so as to prevent the collection thereon of any appreciable quantity o! liquid cathode material.

5. The invention defined in claim 4, wherein said tube forms part of a control grid for the device.

6. The invention defined in claim 4, wherein said tube is substantially cylindrical throughout its length and is Secured to said re-entrant portion by means of a constricting clamp.

'1. The invention defined in claim 4, wherein said narrower re-entrant portion is turned back within the wider re-entrant portion so that the anode seal is nearer the end of the device than the further projecting parts of the re-entrant portion.

8. In a pool cathode electric discharge device having an envelope mainly of vitreous material, a tubular integral re-entrant portion on said envelope, a. plurality of anodes sealed through said re-entrant portion. a tube surrounding said anodes supported directly on and forming with said re-entrant portion a seal impervious to liquid cathode material and bames within said tube separating said anodes, the outer surface of said tube extending from said re-entrant portion aiways towards the cathode so as to prevent the collection thereon of any appreciable quantity of liquid cathode material.

9. The invention defined in claim 8, wherein said tube forms part of a control grid for the device.

10. The invention defined in claim 8, wherein said tube is substantially cylindrical throughout its length and is Secured to said re-entrant portion by means of a constricting clamp.

- DAVID LORIMER SMART.

REFERENCES crrEn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,908,949 Boveri et al. May 16. 1933 2,095,768 Slepian Oct. 12, 1937 2308939 Siemens et al. Jan. 19, 1943 

